diff --git a/doc/pages/Manual.md b/doc/pages/Manual.md
index 9867d394b72..73b62352978 100644
--- a/doc/pages/Manual.md
+++ b/doc/pages/Manual.md
@@ -647,6 +647,10 @@ other system).
   by opam, the new value will replace the old one at the same position instead
   of being put in front.
 
+`FOO = ""` causes `FOO` to be set _but empty_ on Unix but _unset_ on Windows.
+
+`FOO += ""`, `FOO := ""`, etc. are all ignored - i.e. opam never adds empty segments to an existing variable.
+
 ### URLs
 
 URLs are provided as strings. They can refer to:
diff --git a/master_changes.md b/master_changes.md
index c05ff5d9136..d3d2c78a88f 100644
--- a/master_changes.md
+++ b/master_changes.md
@@ -280,6 +280,8 @@ users)
   * Don’t rebuild packages when updating dependencies or availablity, unless the current state needs to be changed [#5118 @kit-ty-kate - fix #4647]
   * Rebuild packages when removing or adding the "plugin" flag [#5118 @kit-ty-kate]
   * Do not rebuild packages when an extra-source's url changes but not its checksum [#5258 @kit-ty-kate]
+  * Correctly handle empty environment variable additions [#5350 @dra27]
+  * Skip empty environment variable additions [#5350 @dra27]
 
 ## Opam file format
   *
@@ -537,6 +539,8 @@ users)
   * Add optional argument `?env:(variable_contents option Lazy.t * string) OpamVariable.Map.t` to `OpamSysPoll` and `OpamSysInteract` functions. It is used to get syspolling variables from the environment first. [#4892 @rjbou]
   * `OpamSwitchState`: move and reimplement `opam-solver` `dependencies` and `reverse_dependencies` [#5337 @rjbou]
   * `OpamEnv`: add `env_expansion` [#5352 @dra27]
+  * `OpamEnv`: fix invalid argument raised when trying to unzip empty string [#5350 @dra27]
+  * `OpamEnv`: skip environment updates and revert with empty strings [#5350 @dra27]
 
 ## opam-solver
   * `OpamCudf`: Change type of `conflict_case.Conflict_cycle` (`string list list` to `Cudf.package action list list`) and `cycle_conflict`, `string_of_explanations`, `conflict_explanations_raw` types accordingly [#4039 @gasche]
diff --git a/src/state/opamEnv.ml b/src/state/opamEnv.ml
index b4adaf04266..85876b8b30d 100644
--- a/src/state/opamEnv.ml
+++ b/src/state/opamEnv.ml
@@ -40,19 +40,19 @@ let unzip_to elt current =
     | ([], rs) -> Some rs
     | _ -> None
   in
-    match split_var elt with
-    | [] -> invalid_arg "OpamEnv.unzip_to"
-    | hd::tl ->
-      let rec aux acc = function
+  match (if String.equal elt "" then [""] else split_var elt) with
+  | [] -> invalid_arg "OpamEnv.unzip_to"
+  | hd::tl ->
+    let rec aux acc = function
       | [] -> None
       | x::r ->
-        if x = hd then
+        if String.equal x hd then
           match remove_prefix tl r with
           | Some r -> Some (acc, r)
           | None -> aux (x::acc) r
         else aux (x::acc) r
-      in
-        aux [] current
+    in
+    aux [] current
 
 let rezip ?insert (l1, l2) =
   List.rev_append l1 (match insert with None -> l2 | Some i -> i::l2)
@@ -91,6 +91,7 @@ let apply_op_zip op arg (rl1,l2 as zip) =
     or empty lists is returned if the variable should be unset or has an unknown
     previous value. *)
 let reverse_env_update op arg cur_value =
+  if String.equal arg  "" && op <> Eq then None else
   match op with
   | Eq ->
     if arg = join_var cur_value
@@ -157,9 +158,13 @@ let expand (updates: env_update list) : env =
             | Some s -> ([], split_var s), reverts
             | None -> ([], []), reverts
       in
+      let acc =
+        if String.equal arg "" && op <> Eq then acc else
+          ((var, apply_op_zip op arg zip, doc) :: acc)
+      in
       apply_updates
         reverts
-        ((var, apply_op_zip op arg zip, doc) :: acc)
+        acc
         updates
     | [] ->
       List.rev @@
diff --git a/tests/reftests/env.test b/tests/reftests/env.test
index a262e13a586..85c2910363b 100644
--- a/tests/reftests/env.test
+++ b/tests/reftests/env.test
@@ -70,6 +70,42 @@ The following actions will be performed:
 Done.
 ### cat $OPAMROOT/build-env/doc/pkg.version
 V1.2.3
+### : empty environment variables update :
+### NV_VARS=''
+### <pkg:nv.1>
+opam-version: "2.0"
+setenv: [
+  [ NV_VARS  += ""    ]
+  [ NV_VARS2 := ""    ]
+  [ NV_VARS3 := ""    ]
+  [ NV_VARS3 := "foo" ]
+  [ NV_VARS4  = ""    ]
+]
+flags: compiler
+### opam switch create emptyvar nv
+
+<><> Installing new switch packages <><><><><><><><><><><><><><><><><><><><><><>
+Switch invariant: ["nv"]
+
+<><> Processing actions <><><><><><><><><><><><><><><><><><><><><><><><><><><><>
+-> installed nv.1
+Done.
+### opam env | grep "NV_VARS" | ';' -> ':'
+NV_VARS3='foo:': export NV_VARS3:
+NV_VARS4='': export NV_VARS4:
+### opam exec -- opam env --revert | grep "NV_VARS" | ';' -> ':'
+NV_VARS3='': export NV_VARS3:
+NV_VARS4='': export NV_VARS4:
+### NV_VARS=/another/path
+### NV_VARS2=/another/different/path
+### NV_VARS3=/yet/another/different/path
+### NV_VARS4=ignored-value
+### opam env | grep "NV_VARS" | ';' -> ':'
+NV_VARS3='foo:/yet/another/different/path': export NV_VARS3:
+NV_VARS4='': export NV_VARS4:
+### opam exec -- opam env --revert | grep "NV_VARS" | ';' -> ':'
+NV_VARS3='/yet/another/different/path': export NV_VARS3:
+NV_VARS4='': export NV_VARS4:
 ### : root and switch with spaces :
 ### RT="$BASEDIR/root 2"
 ### SW="switch w spaces"